In January, at the World Economic Forum in Davos, Switzerland, movers and shakers lined up to spit into test tubes -- the first step to having snippets of their DNA analyzed by 23andMe, a personalized gene-testing company that for $999 promises to help people "search and explore their genomes."

Those wanting an even more complete analysis of their biological inheritance can turn to Knome, a Cambridge, Mass., company that, for $350,000, will spell out all 3 billion letters of their DNA code -- an unparalleled opportunity, the company says, to "Know thyself."

For singles on tighter budgets and with narrower interests, there is ScientificMatch.com, which says that its $995 genetic test will help clients find DNA-compatible mates who will smell sexier to them, have more orgasms and produce healthier children.

This is the world of direct-to-consumer genetic testing, a peculiar mix of modern science, old-fashioned narcissism and innovative entrepreneurialism, all made possible by the government-sponsored Human Genome Project.

More than 20 companies today offer "personalized genomics" tests that promise to help clients discern from their DNA what diseases they are likely to get, whether they are shy or adventurous, even their propensity to become addicted to drugs. A growing number bypass doctors and deal directly with consumers.

The trend has critics warning that the market is becoming rife with hype. The field is effectively free of regulatory oversight, watchdogs note, and much of the science behind the results is still sketchy.

But backers of these enterprises say they are pioneering nothing less than a medical and cultural revolution. With each person who adds his or her DNA to the companies' high-security databases, they say, links between specific gene variants, health conditions and behavioral traits are getting documented, speeding discoveries about biology, identity and destiny.

"We call it consumer-enabled research," said Linda Avey, co-founder of 23andMe, based in Mountain View, Calif. "It's about changing the paradigm of how research is done."

It is also about self-discovery and a new kind of social networking, as "members" -- as some companies call them -- learn about their DNA details and share them with others.

"We envision a new type of community where people will come together around specific genotypes, and these artificial barriers of country and race will start to break down," said Anne Wojcicki, who with Avey co-founded 23andMe.

"I think people will really get into it," said George Church, the Harvard geneticist who co-founded Knome and founded the not-for-profit Personal Genome Project, which will compare the genomes of 100,000 people willing to make their DNA public. "I think this is going to connect people clear around the world."

Gene Chips Slash Costs

Personalized medicine, the detection of people's individual health risks and the tailoring of preventive strategies and therapies just for them, has been a buzzword for years. But it remained elusive until technological advances allowed researchers to scan huge stretches of human DNA quickly and at relatively modest expense.

"Gene chips" that cost just a few hundred dollars can today detect hundreds of thousands of tiny molecular hiccups in a smidgeon of DNA collected from saliva or blood. Unlike better-known genes that single-handedly cause inherited diseases such as sickle cell anemia, most of these gene variants add in very small ways to a person's medical weaknesses or strengths.

Only about 100 such glitches have been convincingly linked to specific diseases or behavioral tendencies, but new connections are being discovered every month. Together they can start to paint a picture of a person's health prospects and behavioral predilections.

Meanwhile, the cost of spelling out an individual's entire genetic code, or genome, is also dropping precipitously, from several million dollars a few years ago to about $1 million last year and an anticipated $200,000 or so this year.

"Our goal and vision has been to make a total human genome affordable," said Christopher K. McLeod, chief executive of 454 Life Sciences in Branford, Conn., which makes some of the fastest and most powerful gene-sequencing machines under the corporate motto "Measuring Life One Genome at a Time."

By comparing an individual's genetic profile with databases of known correlations, companies can calculate that the person, for example, is 30 percent more likely than average to get colon cancer, 20 percent less likely to get cataracts, and 10 percent more likely to be impulsive or have anger-management issues.

Yet the probabilistic nature of those results is potentially problematic, said J. Craig Venter, the geneticist who broke scientific and cultural ground last year when his eponymous Rockville research institute spelled out his entire genetic code and posted the results on a publicly accessible database, revealing to the world that he has, among other things, genetic inclinations toward wet earwax.

It can be entertaining, Venter said, to learn one has a gene for soggy earwax. "But if you're on the receiving end of one of these tests and are told your probability of having a serious problem is 62 percent, what the hell does that mean?"

Results Can Mislead

And that is assuming the results are correct. As it turns out, many gene tests today search for DNA patterns that have been linked to a disease or trait in only one or two studies. Such findings are often overturned by later research.

Even if the findings hold up, there are countless other genes still unstudied that experts say will eventually be found to either augment or counterbalance the risks discovered to date. Until those factors -- harmful and protective -- are added to the gene chips, clients run the risk of being misled.

"This information can be quite profound," said R. Alta Charo, a professor of law and bioethics at the University of Wisconsin. "It can lead to a decision to have your breasts chopped off before you've been sick for a day or having your ovaries scooped out before you have children. These are dramatic decisions, but these products are going on the marketplace as though they were underarm deodorant."

Exacerbating the problem is that virtually no one is watching over the industry. The Food and Drug Administration does not regulate most gene-based tests, and there is no federal proficiency-testing system for companies offering them.

So while some of the new companies, including 23andMe, Knome and Navigenics of Redwood Shores, Calif., boast solid teams of renowned researchers and emphasize that the information they provide is not diagnostic, other outlets inhabit the scientific fringe.

Perhaps most denigrated by experts are those that purport to identify people's nutritional needs from their DNA and then sell them dietary supplements at a hefty profit.

"It is totally bogus," said Gail Geller of the Berman Institute of Bioethics at Johns Hopkins University, whose research has documented how easily the public can be bamboozled by genetic test results.

Then there is ScientificMatch.com, which "uses your DNA to maximize the chances of finding chemistry -- actual, physical chemistry -- with your matches," according to the company's Web site.

At the heart of that claim is a hypothesis that people are most attracted to others whose immune systems differ most from their own. A few studies have found evidence supporting the idea (it may be an evolutionary strategy for maintaining genetic diversity). But at best, geneticists say, it is a narrow basis upon which to choose a mate.

"It creates an air of charlatanism that doesn't help the field," Venter said.

All told, concluded a study in this month's issue of the American Journal of Human Genetics, "There is insufficient scientific evidence to conclude that genomic profiles are useful in measuring genetic risk for common diseases or in developing personalized diet and lifestyle recommendations for disease prevention."

The Science Is Still Young

Despite today's limitations, the day will come, experts agree, when enough will be known about human genetics so that a scan of an individual's genome will convincingly predict that person's medical risks and behavioral foibles -- perhaps with enough assuredness to dictate preemptive therapy or even extend disability rights to some whose behavior falls outside societal norms. But the only way to get there is to collect massive amounts of data from a wide array of people so computers can find those correlations.

That task is underway, but the work takes time, which is why direct-to-consumer genomics companies say they should be welcomed. Most people are disinclined to sign up for research that offers nothing in return, Wojcicki said, but at 23andMe, "they get something back right away, and they are also part of something really powerful."

Wojcicki predicts that as members share information about their genes, their health and their personalities -- an irresistible option for many in this age of electronic "friending" -- the new enterprises will revolutionize health care "the way YouTube revolutionized media."

"I call it the democratization of the genome," Venter said.

Concerns persist. If people want to use their information in a meaningful way, they will probably want to share it with their physician, said Francis S. Collins, director of the National Human Genome Research Institute and a leader of the Human Genome Project, completed in 2003, which cobbled together the first complete human DNA sequence. And medical records are not totally opaque to prying eyes.

"People ought to think about that," said Collins, who confessed to feeling both excited and concerned about consumer-driven genomics. "We don't want employers to use genetic information to make hiring or firing or promotion decisions on the basis of fears that an employee may get sick." It is "enormously frustrating," he added, that bills prohibiting genetic discrimination have been passed by both chambers of Congress but are stalled because of an unrelated power struggle on Capitol Hill.

One subtle but potentially insidious downside of the new trend, Collins said, is that people may slip into the DNA-deterministic thinking that fed the early 20th-century eugenics movement, in which people with "undesirable" traits underwent forced sterilizations.

"I very much worry that all this emphasis on a 'gene for this' and 'gene for that' raises the risk that people will conclude that that's the whole story," Collins said. Instead of empowering people to make healthful changes in their lives, that could simply make them "more fatalistic," he said, "in which case, what's the point?"

At the same time, he and others acknowledged, by identifying people with similar genes but different health outcomes, genomics companies' databases could help scientists identify the specific environmental influences -- diet, exposure to certain chemicals, even stress or abuse -- that interact with particular genes to make people into the individuals they are.

"By disentangling the genetics, we'll get a much deeper appreciation of both nature and nurture," said Church, the Harvard geneticist. "I would be surprised if it didn't change our view of ourselves pretty significantly."

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